Simple Telecommunication System

Network Hierarchy

IC – International Centre
BC – National Centre
TC – Tertiary Centre
SC - Secondary Centre
PC – Primary centre
LE – Local Exchange (Central Office)

The public telephone system consists basically a large number of single telephones unevenly distributed through out of the country, each one being connected to a switching centre called telephone exchange. Each exchanges has lines to other exchanges and also to a suitable positioned main switching centre which in turn has access to all the other main switching centre in the system.Thus, any telephone connected to an exchange can be connected, at will, to any other telephone in the country and by using an international switching centre, to any telephone in the system of any other country.In some countries the Local Exchange is known as the Central Office.

Local Battery (LB)

A local battery powered all the original telephones. This was because the transmitter needed power and the local battery provided the right power irrespective of the length of or bad external wiring.because the batteries were installed in customer premises. This was a major expense for the maintenance team. original batteries xxxere wet cells which could leak and these were letter superseded by dry cells.

Central Battery ( CB)

The ‘LB’ system was superseded by the central Battery System which used a large set of battries at the local exchange and this became possible because of saving made by economics of scale.

‘CB’ Working

Advantages

Easy to maintainInstallation and maintenance cost lost

Disadvantages

Limitations(Distance for line providing)